1. Field of Invention
The present invention relates to disinfecting and sterilizing solutions, and more particularly to a disinfecting and sterilizing concentrate containing an aromatic dialdehyde and a neutral pH buffering system.
2. Description of Prior Art
Aromatic dialdehyde disinfecting and sterilizing solutions are well known in the art. Aromatic dialdehyde solutions have bacteriostatic and fungistatic activity. They are useful for disinfecting or sterilizing medical devices or environmental surfaces. Unfortunately, present aromatic dialdehyde solutions limit the concentration of the aromatic solution to less than or equal to 5 w/w % of the total solution because aromatic dialdehydes have limited aqueous solubility. While water-miscible solvents may increase the solubility of aromatic dialdehyde, the solvents adversely affect the buffering systems of aromatic dialdehyde disinfecting and sterilizing solutions.
Bruckner et al. in U.S. Pat. No. 4,971,999, discuss ortho-phthalaldehyde as the active ingredient in an aromatic dialdehyde disinfecting and sterilizing solution. U.S. Pat. No. 4,971,999 is incorporated herein by reference. They discuss "in-use solutions" and more concentrated solutions. An "in-use solution" contains an effective amount of the active aromatic dialdehyde ingredient and is a solution which is sufficiently dilute for ordinary disinfecting and sterilizing purposes.
Bruckner et al. observe that for "in-use solutions," ortho-phthalaldehyde is normally present in amounts between 0.025 w/w % and 1 w/w %. They also observe that higher concentrations, e.g., up to 2 w/w %, can be used but that the preferred concentration is 0.05 w/w % to 0.5 w/w %. They further observe that higher concentrations may be used for shipping the solution to the point of use and the solution can then be diluted with water to the desired "in-use solution" concentration.
In any event, they note that the limit on the amount of ortho-phthalaldehyde used in the concentrate solution is a function of the solubility of the aromatic dialdehyde in water, which is about 5 w/w %. Bruckner et al. indicate that the concentration may be increased above the 5 w/w % level with the addition of water-miscible solvents. They specifically state that suitable solvents include methanol, ethanol, isopropanol, glycols, tetrahydrofuran, dimethyl sulfoxide, and dioxane. But, Bruckner et al. do not discuss or address any adverse affects caused by the additional solvents. There are some adverse affects.
Bruckner et al. observe that an alkalinating or acidifying salt can be used in the compositions (solutions) as a buffer to maintain a desired composition pH during storage and use. Bruckner specifically discloses an alkali metal carbonate or bicarbonate, e.g., sodium bicarbonate or potassium bicarbonate, or phosphate as a buffering salt. They note that the buffer may be an organic carboxylate salt such as sodium citrate, sodium acetate, potassium hydrogen phthalate, potassium citrate, or potassium acetate, or an inorganic borate salt such as potassium or sodium borate.
While Bruckner et al. contend that the disinfecting properties of the composition are not pH dependent, they do note that the sporicidal activity of an aromatic dialdehyde solution is somewhat pH dependent. They specifically observe this pH dependency at low aromatic aldehyde concentrations (e.g., 0.5 w/w % or less for phthaladehyde). They report that the optimal pH range for sporicidal activity is between 6 and 8 and thereby underscore the importance of buffering.
Moreover, the pH range from about 6 up to about 8 is preferred to ensure materials compatibility of certain medical instruments or utensils. Certain medical instruments or utensils are prepared from materials such as anodized aluminum, carbon steel, and rubber. These materials are chemically incompatible with environments outside the pH range from about 6 up to about 8. Therefore, to prevent harm to medical instruments or utensils prepared from these materials, a buffering system is required to maintain a pH in the range from about 6 up to about 8.
Unfortunately, the concentration of water-miscible solvents required to increase the concentration of the aromatic dialdehyde above 5 w/w % are generally incompatible with the buffering system of the aromatic dialdehyde solutions. That is, as the concentration of the aromatic dialdehyde is increased by the addition of water-miscible solvents, the physical stability of the buffering system is diminished. This physical instability is particularly apparent with phosphate buffering systems. To achieve and maintain the desired pH range from about 6 to about 8, the concentration of the buffering system must be increased as the concentration of aromatic dialdehyde is increased. Accordingly, there is a need to increase the concentration of the aromatic dialdehyde and the concentration of the pH buffering system while maintaining the physical stability of the pH buffering system. In other words, there is a need to stabilize the buffering systems of concentrated aromatic dialdehyde solutions against the water-miscible solvents used to increase the concentration of the aromatic dialdehyde. Throughout the entire process, there is, of course, a need to ensure the chemical stability of the aromatic dialdehyde.